Issue 1726 sumvar

[valentinsulzer]

Description

Add model.summary_variables so that the user can set which summary variables they want. This also makes the half-cell model and lead-acid models compatible with experiments.

Fixes #1726

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov]

Codecov Report

Merging #1760 (4bab6a5) into develop (f2c36a1) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop    #1760   +/-   ##
========================================
  Coverage    99.28%   99.28%           
========================================
  Files          343      343           
  Lines        18900    18921   +21     
========================================
+ Hits         18765    18786   +21     
  Misses         135      135           

Impacted Files	Coverage Δ
...m/models/full_battery_models/base_battery_model.py	99.71% <100.00%> (+0.01%)	⬆️
...ttery_models/lithium_ion/base_lithium_ion_model.py	100.00% <100.00%> (ø)
pybamm/solvers/solution.py	100.00% <100.00%> (ø)

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[brosaplanella]

Looks good, thanks Tino!